For several years glycol has been used by airports around the world to de-ice the wings of aircraft prior to take-off during poor winter weather conditions. In recent years, the presence of glycol contamination in the ground water table surrounding airports has been discovered. Since the discovery, new controls and regulations have been introduced whereby aircraft are sprayed with glycol at de-icing stations and the sprayed aircraft then taxi for priority take-off. At these stations, glycol that drips off the aircraft is collected along with water melted in the de-icing from freezing rain or snow that may be falling due to poor weather conditions. Since glycol forms a miscible solution with water, the solutions collected may have water contents as high as 95% water to 5% glycol. Currently, the collected solution is removed from the de-icing station for waste management treatment which can involve distillation of the water from the glycol to recover the glycol.
Distillation of water from a water and glycol solution is the most common method used to remove water from a solution of water and glycol. Such distillation systems are used in natural gas treatment systems where the glycol is used to treat natural gas to remove water from natural gas and then the water and glycol solution is distilled by a variety of heating methods to remove the water from the glycol. In such systems the water content in the water and glycol solution is usually well below 10% and the distilled solution ends up being in the order of 99% or better glycol. Examples of these natural gas water removal and subsequent water distillation systems are disclosed in U.S. Pat. Nos. 4,332,643 issued Jun. 1, 1982 to Laurence S. Reid; 4,322,265 issued Mar. 30, 1982 to Harold S. Wood; 4,010,065 issued Mar. 1, 1977 to Carl E. Alleman; 3,841,382 issued Oct. 15, 1974 to Charles K. Gravis, III et al; 3,450,603 issued Jun. 17, 1969 to Charles O. Meyers et al; and, Canadian Patent 807,953 issued Mar. 11, 1969 to Clifford W. Barnhart.
It is also known to purify glycol contaminated by oxidation products by adding small amounts of water and distilling off the water under partial vacuum. Such a method is disclosed in U.S. Pat. No. 3,398,061 issued to Horst Taul et al.
It should be understood that the above methods of distillation involve the use of heat to vaporize the water in glycol solutions having less than 10% initial water content. There is no teaching of using distillation methods to remove water from a glycol and water solution having as much as 95% water content.
It is also known to provide evaporation towers in which human waste, corrosive solutions and saline water are purified by heated packing mediums within the towers. Such evaporation towers are disclosed in U.S. Pat. No. 5,207,869 issued May 4, 1993 to H. David Harmoning et al; Canadian Patent 1,005,746 issued Feb. 22, 1977 to Roger Rat et al; and Canadian Patent 976,866 issued to Melvin H. Brown. However, the application of these evaporation towers is not relevant to the removal of relatively high initial concentrations of water from a water and glycol solution.
There is still a need for a relatively energy efficient apparatus for the removal of water from water and glycol solutions having high initial concentrations of water so that ultimately a reusable water and glycol solution may be obtained.